This invention relates generally to color video signal recording and/or reproducing systems, and more particularly to systems for recording and reproducing, with a large signal to noise (S/N) ratio, color burst signals of color video signals.
In general, it is necessary to correct the phase of a carrier chrominance signal in a color video reproducing system. In this case, the phase of the color burst signal within the reproduced signal is detected. The phase correction is carried out responsive to the resulting detection output.
Accordingly, in order to correct the phase accurately and positively, it is necessary that the color burst signal be recorded and reproduced with a large S/N ratio and in a stable manner.
Therefore, a previous system used an automatic gain control circuit which operated only during the periods when a color burst signal was present. The color burst signal is always recorded at a constant level which is optimum for recording. However, since a color burst signal does not exist in a black-and-white (monochrome) video signal, the high-frequency component of the monochrome video signal is amplified to an abnormally high level by an automatic gain control circuit. A deleterious effect is produced in the luminance signal.
For this reason, it is necessary, in this system, to provide a so-called color-killer circuit for detecting the presence or absence of a color burst signal and for cutting off the carrier chrominance signal transmission system, at the time when there is no color burst signal. However, this color-killer circuit is complicated, and the recording system cannot be produced at low cost. Furthermore, if there is a monochrome input video signal with a small S/N ratio, a noise component is erroneously detected as a color burst signal. The color-killer circuit does not operate normally despite the introduction of a monochrome video signal.
Accordingly, another system avoids use of a color-killer circuit. The peak value (maximum level value) of the entire chrominance signal is detected at the time of recording. Automatic chroma control (hereinafter referred to as ACC) is carried out. The ACC circuit in this system detects the peak value of the color burst signal. The ACC operation occurs when the amplitude of the carrier chrominance signal is less than the amplitude of the color burst signal. Conversely, if the amplitude of the carrier chrominance signal is greater than the amplitude of the color burst signal, the ACC circuit detects the peak value of the carrier chrominance signal, to carry out the ACC operation. For this reason, the amplitude of the color burst signal is disadvantageously varied by the magnitude (saturation) of the amplitude of the carrier chrominance signal. The amplitude of the color burst signal cannot be continually controlled at a constant amplitude, whereby color shading is produced.
Accordingly, we have solved the problems accompanying the previously conceived systems, as described above, and have devised the improved system of the present invention.